1. Field of the Technology
The disclosed technology relates to a photovoltaic cell and a photovoltaic module employing such photovoltaic cells and, more specifically, to a photovoltaic cell structure excellent in photo-electric conversion efficiency.
2. Description of the Related Art
As a conventional photovoltaic cell is known a photovoltaic cell which includes a light receiving surface electrode and a rear electrode provided on opposite sides of a silicon substrate having a pn junction, and a module thereof (see, for example, Japanese Unexamined Patent Publication No. HEI10-107306 (1998)).
In such conventional photovoltaic cell, a grid pattern (of a comb shape) which includes thin lines and thick lines intersecting each other is employed as the light receiving surface electrode for increasing a light receiving area as much as possible.
On the other hand, the rear electrode is an electrode formed by applying an electrode material paste mainly containing aluminum over the entire rear surface of the silicon substrate by printing and then firing the applied paste.
In the photovoltaic module, the photovoltaic cells are two-dimensionally arranged, connected in series with a light receiving surface electrode of one of each two adjacent photovoltaic cells being connected to a rear electrode of the other photovoltaic cell by a wiring material such as a copper ribbon, and properly sealed with a glass plate or a moisture-proof film.
In the field of the photovoltaic cells, the thickness of the silicon substrate has been reduced for reduction of production costs, and a silicon substrate having a reduced thickness on the order of 300 μm has been generally used.
For further reduction of the production costs, it is conceivable to further reduce the thickness of the silicon substrate. Where the thickness of the silicon substrate is reduced to about 250 μm or smaller, however, incident light of a long wavelength range is not sufficiently absorbed by the silicon substrate, thereby mostly reaching the rear surface of the silicon substrate.
The incident light of the long wavelength range reaching the rear surface of the silicon substrate is reflected on the rear electrode back into the silicon substrate.
Where the rear electrode is the electrode formed in the conventional manner by firing the electrode material paste mainly containing aluminum, however, the reflectivity thereof is merely about 70%.
Therefore, the reduction of the thickness of the silicon substrate reduces the production costs, but fails to provide a sufficient photo-electric conversion efficiency.